That is nonsense.
Any President who even suggested re-engaging US combat troops in RVN after 1972 would have been dragged out of the White House and lynched by enraged mobs of US citizens - and the Army may very well have refused orders to do it.
The best we could have done is maintain a peaceful transition to a unified Vietnam.
And we could have avoided the human tragedy of boat people, re-education camps, the killing fields, and 58,000 young Americans deads, and arrive at the same place we are now, normalizing relations and trading freely with Vietnam.
But we had to have the CIA 'S war. Got a bunch of people, like the Bushes, rich.